The structure of a disposable diaper is disclosed, for example, in Japanese Patent Kokai No. 11[1999]-285,510. In the structure of this disposable diaper an elastic strand(s) is provided at various locations including at the bending section and free ends of a sheet so as to form a barrier. In the process of producing disposable diapers with this kind of structure, the disposable diapers are produced through steps such as applying an adhesive to elastic strand material being fed continuously, then bonding the elastic strand material to a base or substrate material which forms the main part of the diaper and which is also fed continuously, and finally in a subsequent step cutting the resulting product into individual diapers.
Not only in the production of the aforesaid disposable diapers but also in the process of producing, for example, disposable surgical gowns to be used in operating rooms, elastic strand material and nonwoven or woven fabrics are bonded together with an adhesive. Also, in a process of this kind, the materials to be coated with the adhesive are not always elastic members, there are cases where strand materials with no stretching properties are coated with the adhesive and bonded to a substrate. Accordingly, the term “strand material” or similar terms as used in the present specification are meant to also include both elastic materials such as elastic yarn and nonelastic material.
Furthermore, the cross-sectional shape of the strand material is not only circular but includes various shapes such as elliptic, square, and rectangular, and the thickness also ranges from the order of hundredths of a millimeter to the order of several millimeters. Thus, there are no particular limitations with regard to the shape and thickness of the strand material. As the adhesive to be used, a hot-melt adhesive is used in many cases, but other types of adhesive can be used as well.
A conventional device and method for applying an adhesive to strand material in the process of producing the aforesaid disposable diapers or other products will now be explained with reference to FIGS. 9-12. FIG. 9 shows a front view of the conventional coating device. FIG. 10 shows a vertical sectional view of the conventional coating device. FIG. 11 shows an expanded view of the leading end portion of FIG. 10. FIG. 12 shows an enlarged view of encircled portion D of FIG. 9.
In FIGS. 9-12, coating device 51 includes a valve mechanism 65 which is opened and closed by operating air 80. A gun body 52 forms the coating device 51; a cylinder block 53 is attached with a plurality of bolts 54 to the top of the gun body 52, and a piston 55 moves up and down and is located inside the cylinder block 53. A valve stem 56 is fastened to the piston 55 and is extended into a liquid chamber 59 through a seal block 57. A seal member 58 is provided in the gun body 52, and includes a valve ball 60 at the leading end.
Furthermore, a valve seat member 62 that has an outlet 62a is attached with a plurality of bolts 63 to the lower part of the gun body 52. A screw 62b is provided in the lower outer diameter section of the valve seat member 62. The valve ball 60 is at the leading end of the valve stem 56 and the valve seat member 62 forms the valve mechanism 65. A spring 75 is placed between the large-diameter section at the leading end of the valve stem 56 and the underside of the seal block 57, and closes the valve mechanism 65 by forcing the valve stem 56 downward at all times.
A nozzle member 66 has a flange section 66a. A cap nut 67 is provided with a small-diameter section 67a to be engaged with the flange section 66a of the nozzle member 62 and a screw section 67b to be engaged with the screw 62b of the valve seat member 62. The nozzle member 66 is attached to the lower end of the valve seat member 62 by engaging the small-diameter section 67a of the cap nut 67 with the flange section 66a, and attaching the screw section 67b of the cap nut 67 over the screw 62b. 
Moreover, a flat section 66b is formed in the nozzle member 66, and a nozzle plate 68 is fastened with a plurality of bolts 69 to the flat section 66b. A through-hole 66c communicates with the outlet 62 of the valve seat member 62. A horizontally long groove 66d extends in the horizontal direction in communication with the through-hole 66c and opens to the flat section 66b, and three branched nozzle grooves 66e communicate with the horizontal groove 66d in the nozzle member 66. The horizontal groove 66d and the nozzle grooves 66e are combined in such a way that the nozzle plate 68 covers the open section of the grooves. The nozzle groove 66e is open at the lower end and a nozzle hole 70 couples with the nozzle plate 68.
The lower ends of the nozzle member 66 and the nozzle plate 68 have exactly the same shape, and are formed like teeth of a comb stretching to below the nozzle hole 70. An inverted V-shape groove 61 with its lower end slightly spreading is formed with the nozzle hole 70 at the center. This groove 61 plays a role as a guide for the strand material 14 to be coated with the adhesive. An example of the conventional coating device shown in the figures is a device wherein three nozzle holes 70 are formed so as to apply three strands 14 simultaneously by one coating device 51. The device is not limited to this and may have one nozzle hole or many more nozzle holes to enable the coating of one or more strands.
To return to the explanation of the gun body 52, the gun body 52 is provided with an air through-hole 52a for feeding operating air 80 to the underside of the piston 55, and an adhesive through-hole 52b for feeding an adhesive 81 to the liquid chamber 59. The gun body 52 is fastened with a plurality of bolts 72 to a manifold 71. The manifold 71 is provided with an air feed hole 71a that communicates with the air through-hole 52a of the gun body 52, and an adhesive feed hole 71b that communicates with the adhesive through-hole 52b. An operating air feed device 73 is connected with the air feed hole 71a of the manifold 71 via a tubular path such as a hose, and an adhesive feed device 74 is connected with the adhesive feed hole 71b of the manifold 71 via a tubular path such as a hose.
In the coating device thus constructed, the adhesive 81 fed from the adhesive feed device 74 is stored in the liquid chamber 59 through the adhesive feed hole 71b of the manifold 71 and the adhesive through-hole 52 of the gun body 52. If operating air 80 is fed from the operating air feed device 73 to the underside of the piston 55, the piston 55 and valve stem 56 operate upward against the force of the spring 75, and the valve mechanism 65 is opened.
While the valve mechanism 65 is open, the adhesive 81 in the liquid chamber 59 is extruded from the nozzle hole 70 via through-hole 66c of the nozzle member 66 and the horizontally long groove 66d from the outlet 62a of the valve seat member 62, and applied to the surface of strand material 14. In this case, the nozzle hole 70, the topmost part of the inverted V-shape grooves 61 of the nozzle member 66 and nozzle plate 68 are in contact with the strand material 14. The strand material 14 is coated with the adhesive 81 and adhered to the substrate in a not-illustrated device in a later step. If the feeding of operating air 80 is stopped and the air pressure on the underside of the piston 55 is released, the valve mechanism 65 closes by the force of the spring 75, and the extrusion of adhesive 81 from the nozzle hole 70 stops. The adhesive can be applied intermittently by the opening and closing operations of the valve mechanism 65.
In another known device, the adhesive is dispensed in a spiral pattern towards the strand material. One or multiple strands can be used and the adhesive can be dispensed from one or multiple nozzles. The spiral pattern of adhesive wraps completely around the strand material while the strand material is still separate from the substrate. The operating characteristics of this system such as adhesive pressure, air pressure, distance from the dispenser nozzle to the strand material can all be varied to control the extent of the wrap around and to control the amount of adhesive captured by the strand material. It is well known to those of ordinary skill in the field that the strand material can capture substantially all of the spiral adhesive or some portion of the spiral adhesive can pass by the strand material to contact the substrate. This known device is described in U.S. Pat. No. 4,842,666 and as shown in “Adhesive and Powder Application Systems for the Nonwoven Industry”, Nordson Corporation, October 1992, both of which are incorporated herein by reference.
The first aforementioned adhesive coating device is known to have the following problems. If the thickness or shape of the strand material changes, the size of the inverted V-shape groove also must be changed, and this leads to troublesome operation and extra time. Furthermore, since the strand material is coated with the adhesive in constant contact with the nozzle hole and inverted V-shape groove while being transferred at high speed (usually 70-400 m/minute), stress develops in the strand material. As a result, the strand material can be severed, or the grooves of the nozzle member can wear during lengthy operation and become larger than the diameter of the strand material. In some cases the adhesive drips from the strand material onto the substrate.
Furthermore, although the adhesive is applied sufficiently to the area facing the nozzle hole of the strand material, the adhesive is not applied sufficiently to the opposite underside, and this can result in poor adhesion. Moreover, because fiber products are being transferred at high speed, the operating environment is such that fine fibrous dust is more easily formed by friction between the fiber products and mechanical devices. This fine airborne dust adheres readily to the nozzle hole sections, and this adhered dust piles up over time, solidifies, and destabilizes the coating process. In an extreme case, the extrusion of the adhesive becomes obstructed and the strand material can be severed.
Yet another problem has been that, when applying the adhesive intermittently by controlling the opening and closing of the valve mechanism, the adhesive remaining downstream from the valve mechanism is inevitably drawn out by the strand material even after the valve mechanism is closed, and a poor final coating results.
In the second known device mentioned above, the spiral pattern is sometimes difficult to control across the length of the strand material. This can lead to uneven or nonuniform application of the spiral bead of adhesive to the strand material.
Thus, the invention of the present application was developed in view of the above-mentioned problems, and is aimed at providing a device and a method for applying an adhesive to material such as strand material, which requires no change in the device even if the thickness or shape of the strand material is changed, by installing the coating device in noncontact with the strand material. The present invention can achieve good all-around attachment of the adhesive, and moreover can carry out high-quality application of the adhesive with clean nozzles without any adhesion of dust and while maintaining a more uniform back and forth or vacillating adhesive bead pattern.